1. Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus including the same, and, more particularly, to a zoom lens that is, for example, suitable for an image pickup apparatus using a solid-state image sensor such as a video camera, an electronic still camera, a broadcasting camera, a monitoring camera, or for an image pickup apparatus such as a camera using a silver-halide film.
2. Description of the Related Art
In recent years, image pickup apparatuses such as a video camera, a digital still camera, a broadcasting camera, and a monitoring camera using a solid-state image sensor, and a camera using a silver-halide film have been highly advanced, and the entire units thereof have been downsized. Therefore, a compact (small) zoom lens having a short total lens length with a high zoom ratio (high variable magnification ratio) and a high resolution is required as a photographic optical system used for the image pickup apparatuses.
As a zoom lens that meets the needs, a positive-lead type zoom lens in which a lens unit having a positive refractive power is arranged at an object side is known. As the positive-lead type zoom lens, a five-unit zoom lens including five lens units having positive, negative, positive, negative, and positive refractive powers in order from an object side to an image side is known (U.S. Pat. Nos. 6,404,561, 7,177,092, and Japanese Patent Application Laid-Open No. 2007-219040).
Typically, in order to downsize the entire zoom lens as well as to realize a high zoom ratio of the zoom lens, a refractive power of a main variator lens unit is increased and an amount of movement of the main variator lens unit during zooming is increased. When the refractive power of the main variator lens unit is increased and the amount of movement is increased, it becomes easy to realize a high zoom ratio. However, an aberration variation during zooming increases, and it becomes difficult to obtain high optical performance over the entire zoom range.
To realize the high zoom ratio and the downsizing of the entire lens system as well as to obtain the optical performance in the above-described five-unit zoom lens, it becomes important to appropriately set a movement condition and the like according to the refractive power or zooming of each lens unit.
Especially, it becomes important to appropriately set, during zooming, a variation of an air distance between a third lens unit and a fourth lens unit, a variation of an air distance between the fourth lens unit and a fifth lens unit, a refractive power (the reciprocal of a focal length) of a first lens unit and the fourth lens unit, and the like. If these configurations are not appropriately set, it becomes exceedingly difficult to realize the downsizing of an effective diameter of a front lens, to ensure the high zoom ratio, as well as to obtain the high optical performance over the entire zoom range.
In any of the five-unit zoom lenses discussed in U.S. Pat. Nos. 6,404,561, 7,177,092, and Japanese Patent Application Laid-Open No. 2007-219040, a distance between the first lens unit and the second lens unit increases, and a distance between the second lens unit and the third lens unit decreases during zooming from a wide-angle end to a telephoto end. Further, zooming is carried out in such a way that each lens unit is moved to increase a distance between the third lens unit and the fourth lens unit and to increase a distance between the fourth lens unit and the fifth lens unit. Any of the five-unit zoom lenses discussed in U.S. Pat. Nos. 6,404,561, 7,177,092, and Japanese Patent Application Laid-Open No. 2007-219040 has an approximately 10× zoom ratio, and the zoom ratio is not necessarily sufficient. Further, a total lens length from a lens surface closest to the object side to an image plane at a wide-angle end is relatively long and is approximately 13 to 16 times a focal length at the wide-angle end, and the total lens length is more likely to become longer.